1. Field of the Invention
The present invention relates to an image recording apparatus in which an unfixed image is borne by an image bearing member and is then fixed onto said image bearing member, and more particularly to an image recording apparatus in which the unfixed image is electrically borne by the image bearing member.
2. Description of the Prior Art
In conventional image recording apparatus such as electrophotographic apparatus, the transport means for transporting an image bearing member on which an unfixed image is deposited in an image depositing station, for example an image transfer station, from said image depositing station to a fixing station is generally provided with guide members positioned close to said fixing station for guiding said image bearing member having said unfixed image into said fixing station, and there have been proposed various improvements on said guide members for preventing wrinkles eventually formed on said image bearing member in said fixing station or defective image fixation resulting from eventual scattering of the unfixed image. However such improvements on the guide members for guiding the image bearing member in sliding motion to the fixing station have principally been directed to the reduction of the contact resistance with the image bearing member or to the facilitated introduction of the image bearing member into the paired fixing rollers by means of modified shape of the guide members, and there have been proposed no improvements on the guide members relating to the electric charge borne by the image bearing member.
Also with respect to other members relating to the transport between said image depositing station to the fixing station, there have been proposed no improvements based on electrical analysis for example of the scattering of the unfixed image.
It has however been found that the electrical properties of such guide members are of unignorable importance for further improvement of the image quality. For example a visible image formed on a photosensitive drum after image development is subjected to a high voltage of ca. 7 kV by a transfer charger in the image transfer step onto an image bearing member in an electrophotographic copier to provide the image bearing member, from the rear face thereof not facing the photosensitive drum, with a charge of a polarity opposite to that of the developer, whereby the visible image of said developer is transferred from said photosensitive drum to the image bearing member, thus forming an unfixed image thereon. In the above-mentioned procedure the image bearing member is given a charge of ca. 1 kV on the rear face thereof. Said charge on the rear face, though being variable by the voltage applied by said transfer charger, by the spacing of the image bearing member or by the area of image bearing member occupied by the developer, is generally larger than that on the face bearing the unfixed image. Consequently the image bearing member having the unfixed image is electrically unbalanced with respect to the amounts of charge present on the front and rear faces thereof.
The image bearing member in such state can be stably transported for example on a conveyor belt because of electrostatic adhesion of the image bearing member to the conveyor belt. However, at the transfer of the image bearing member with the unfixed image from said conveyor belt to the guide members of the fixing station, there results frictional charging because of the frictional contact between said image bearing member and said guide members. In order to reduce the contact resistance there has been proposed to provide the contact face of said guide member with ribs or with a Teflon coating.
There have however been found certain difficulties which cannot be avoided by such improvements. In case the developer constituting the unfixed image is of a weak coagulative force between the developer particles or of a weak adhesive force to the image bearing member due to a weak electrostatic charge of the developer, the unfixed image is susceptible to the effect of external or above-mentioned frictional charge, causing deterioration, such as scattering, of the image. In case said guide members are electroconductive, the charge present on a face of the image bearing member contacting said guide members is dissipated to said guide members, and the resulting electric field disturbs the image. On the other hand in case said guide members are made of a highly insulating material, the charge resulting from the above-mentioned frictional charging is gradually accumulated on a face of the guide member contacting the image bearing member, giving rise to an electric field causing a perturbation to the unfixed image. Furthermore, if it is attempted to eliminate said charge or the charge present on the rear face of the image bearing member, the image may again be disturbed by an electric field eventually formed at such elimination. Such charge accumulation also depends significantly on the charge present on the face of the image bearing member contacting said guide members, in addition to that resulting from the frictional charging. Such difficulties are also observable in case the particles constituting the unfixed image have a strong adhesive force among themselves or to the image bearing member.